1. Field of the Invention
The present invention relates to a sparking plug cap for internal combustion engines.
2. Description of the Related Art
A recent tendency to higher power output of internal combustion engines leads to higher electrical voltage applied to sparking plugs and higher temperature around the engine. Thus the stringent requirement has been made for qualities of sparking plug caps, for example, the insulation durability thereof at high temperature, further the insulation durability thereof at high temperature under high humidity or in the presence of water.
Conventional sparking plug caps are made of, for example, unsaturated polyesters or polybutylene terephthalate, etc. However, the plug caps prepared from such materials cannot meet the above stringent requirement.
A sparking plug cap using polyphenylene sulfide which is a heat resistive polymer is also suggested (see Japanese Utility Model Kokai No. 43259/1991). However, it is not sufficient in dielectric strength, i.e., insulation durability, at high temperature under high humidity.